Vehicles are equipped with an evaporative emission control system that traps fuel vapors from the fuel tank of the vehicle and stores them in a canister in which charcoal particles or other suitable media are disposed. The fuel vapors are absorbed onto the charcoal particles. To avoid overloading the canister such that the charcoal particles have no further capacity to absorb fuel vapors, the canister is purged regularly.
In a naturally-aspirated internal combustion engine, the pressure in the intake manifold is depressed. This vacuum is used to draw fresh air through the canister. The vapor-laden air is then inducted into the engine and combusted. A purge valve or port is provided that fluidly couples the canister with the intake of the engine when purging is desired.
In boosted engines, i.e., turbocharged, supercharged, or boosted by any suitable device, pressure in the engine's intake is often above atmospheric thereby reducing the available times for purging. To obtain a vacuum to drive purge flow, a tube with a throat (reduced diameter section) causes a higher flowrate which causes the vacuum. The component in which the throat is included is called an ejector or an aspirator.
An example of a prior art configuration in FIG. 1. An engine 10 has an air intake system including a manifold 12 and a throttle body 14. Throttle body 14 has an air passage 16 and a throttle valve 18 to control the quantity of air flowing into manifold 12. Throttle body 14 has an inlet 20 fluidly connected to an outlet 22 of a turbocharger assembly 24.
Turbocharger assembly 24 includes a compressor 26 and a turbine 28. Compressor 26 and turbine 28 are both mounted upon a common shaft 30. Exhaust gases are directed through a duct 32 to turbine 28 and discharged through an outlet tube 34.
Compressor 26 receives air from an inlet duct 36. Air is pressurized by compressor 26 and discharged into outlet 22 and then into throttle body 14 or charge air cooler into manifold 12 and then into engine 10.
Modern engines are equipped with vapor emission control systems which include a fuel vapor storage canister 38. Vapor storage canister 38 has a quantity of activated charcoal particles 40 or other suitable adsorbent material. Activated charcoal absorbs fuel vapor and stores them. Charcoal particles 40 are secured between a lower screen 42 and an upper screen 44. Fuel vapors and air are routed to the interior of canister 38.
Charcoal 40 has a finite storage capacity of fuel vapor. Therefore, the canister is purged periodically to remove fuel vapor from the charcoal by drawing air from the atmosphere into the canister and through the activated charcoal bed. Atmospheric air flows through picks up molecules of fuel vapor in an adsorption process. The fuel laden air is drawing into combustion chambers of engine 10 and burned. An air inlet 46 is provided to allow purge air to engine canister 38. Air from inlet 46 passes downward through a duct 48 to a space 50 beneath the screen 42 and above the bottom of canister 38.
Canister 38 has an outlet opening 52 to allow purge air and fuel vapors to be discharged from canister 38. Normally, purge air and fuel vapor is desorbed from the charcoal through a conduit 54 to either of conduits 56 or 58; alternatively, the conduit can be coupled to the intake manifold. When engine 10 is idling, throttle valve 18 assumes a position 18′ and the interior of throttle body 14 downstream of throttle valve 18 is at a vacuum. During this period, purge air is drawn from conduit 56 through an orifice 60. Excessive purge can interfere with engine performance. A fuel vapor management valve 62 controls air-fuel vapor purge based on engine operating conditions into intake manifold 12.
When engine 10 is operating at part throttle, i.e. with throttle valve 18 between the idle position and wide open throttle (position shown as element 18 in FIG. 1). The portion of throttle body 14 upstream of throttle valve 18 is exposed to manifold vacuum pressure. This vacuum includes air flow through conduit 58, check valve 64, an orifice 66, and port 68 into throttle body 14. Purge flow is influenced by the relative position of throttle valve 18 to port 68 and by the size of the orifice. Orifice 66 limits the purge air flow into engine 10 as appropriate for good operation.
When engine 10 is operating under boost conditions, compressor 26 generates a greater pressure at outlet 22 of turbocharger 24 than at inlet 36. Under these conditions, compressor 26 generates a positive pressure in throttle body 14 and in manifold 12. Check valves 62, 64 prevent air flow from throttle body 14. The positive pressure at outlet 22 causes air to flow through a conduit 70 to an inlet end portion 72 of an ejector 74. Ejector 74 includes a housing defining inlet end portion 72, outlet end portion 66 and a reduced dimension passage 78 (throat) there between. Air passes from inlet 72 through throat 78 to an outlet 76 and then through conduit 80 to inlet 36 of compressor 26. Flow of air through throat 78 reduces pressure as is well known by one skilled in the art.
Ejector 74 also includes a purge air passage 82 which opens into passage 78. Conduit 54 is connected to the purge air passage of ejector 74. A check valve 84 allows the flow of air and vapors from conduit 54 into passage 82 and then into passage 78. Finally, purge air and vapor pass through conduit 70 into throttle body 14 and then into engine 10. During non-boost operation of engine 10, check valve 84 prevents air flow from ejector 74 back to canister 38.
The above-described emissions control operates effectively to route purged vapors to engine 10 and treatment by a catalytic converter (not shown). However, under some conditions, it is undesirable to purge canister 38. For example, when the catalytic converter is too cool to effectively process exhaust gases, provision is made to prevent canister purging. A control valve 86 is provided downstream of outlet opening 52 from canister 38. Valve 86 has an outlet port 88 formed by a valve seat 90. A movable valving member such as a diaphragm 92 is normally positioned by a spring 94 against seat 90 so that air cannot flow through valve 86. This is the condition of the valve when no purge is desired as mentioned above.
When air flow through valve 86 is desired, a vacuum pressure is introduced into valve 86 above the diaphragm 92 which unblocks port 88. Vacuum is directed to valve 86 through a conduit 96 which is connected to a port of a solenoid controlled on-off valve 98. Another port of valve 108 is connected to a conduit 100. In turn, the conduit is connected to a conduit 104. An electric solenoid valve 108 is connected to a conduit 100. In turn, conduit 100 is connected to check valve 102 which is connected to a conduit 104. When open, vacuum is communicated to the space above diaphragm 92 thus allowing purging. When closed, no vacuum is routed to the space above diaphragm 92 thus allowing purging. When closed, no vacuum is routed to the space above the diaphragm and port 88 is blocked thus preventing purging of canister 38. Solenoid valve 108 is commanded to energize by an engine electronic control unit 110 (ECU).
The componentry shown in FIG. 1 is provided merely as background to the present disclosure and is not intended to be limiting in any way. The components are known to be coupled in alternative ways to that shown in FIG. 1.
Ejector 74 of FIG. 1 suffers from multiple deficiencies. It is a stand-alone part that must be separately packaged, protected from damage, and supported. It is known to mount an ejector on an engine intake component, such as shown in FIG. 4. Referring first to FIG. 2, an ejector 120 is shown that has a flange 122 through which tubes 124 and 126 extend. Ejector 120 is shown in cross section in FIG. 3. Disposed in tube 124 is an insert 130 with a reduced cross section. Insert 130 has a throat 132 with a small cross section. The speed at which gases move through throat 132 is much greater than the speed of the flow at an inlet of tube 124. Downstream of insert 130 is a straight section 136. It would be preferable to have this be a diverging tube. Prior art manufacturing methods led to tube 136 being straight. Tube 134 couples to tube 124 at the location of throat 132 via a tee tube 134 to thereby induce flow through 126. In the fabrication of ejector 120, the inside diameter of tube 134 is formed through an orifice proximate a plug 128. After fabrication, tee tube 134 is sealed via plug 128. Ejector 120 is shown mounted to an air box 150 in FIG. 4.
The ejector system shown in FIG. 4 presents some deficiencies. Referring to FIG. 4, the depth that the ejector extends into air box 150 is shown by numeral 140 and the width of ejector 120 within air box 150 is shown by numeral 142 in FIG. 3. This presents considerable encroachment on the interior of air box 150. Air boxes have unique designs depending on the engine, the vehicle, and other package considerations such as other accessories. Although it would be desirable for a vehicle manufacturer to have three or four standard air boxes, in reality, there is little crossover among different vehicles. It is likely that many unique ejectors would be required to mate to a variety of air boxes. The considerable encroachment can also cause higher flow restriction for the air passing through the duct. The ejector of FIGS. 2-4 has three elements: the main body of ejector 120, a cap 144, and insert 130. Insert 130 is sometimes molded separately to avoid a molding process in which a thin pin is used to form the opening. A tube 136 downstream of insert 130 is straight because a pin is pulled to form tube 136. This is not the preferred shape, simply what is available based on the manufacturing process. Disadvantages in the prior art include: the requirement of molding a separate piece for the insert and a plug; obtaining an ejector with less than desired flow characteristics (due to having straight section downstream of the throat); and the resulting ejector is bulkier than desired.
An ejector that is compact and easy to manufacture while maintaining tight tolerances, particularly in the throat area, is desired.